While a variety of techniques can be used to connect annular members of the aforedescribed type to respective shafts, e.g. flange couplings, keys, force fitting, beam and weld connections, it is a common practice to secure the hub of such an annular member to the shaft by a wedging action developed by translating axial force into radial forces.
For example, a sleeve of a wheel, pulley or the like may be fitted onto the shaft and surrounded by an annular wedge having at least one frustoconical surface juxtaposed with a frustoconical surface of a support ring or disk adapted to take up radial stress.
When the wedging ring is forced axially between the disk and the hub, e.g. by a multiplicity of angularly equispaced screws or bolts extending parallel to the axis of rotation and connected, for example, to an oppositely inclined wedging ring, outward radial forces are applied to the disk which are equivalent to inward radial or compression forces which press the sleeve or hub against the shaft and thus provide a friction-tight fit of the hub upon the shaft.
The wedge thus functions as a direction-changing mechanism whereby the axial forces generated by tightening of the screws or bolts are transformed into radial forces which react against the support ring or disk and thus permit the sleeve to be compressed against the shaft.
In the foregoing description, the support ring or disk, the frustoconical wedging surfaces and the wedging ring or rings have been described as elements separate from the shaft or hub. Of course the same principles can apply to the shaft form part of the clamping system. For instance, the wheel or hub can form the support ring and can be provided with frustoconical surfaces directly engaged by the frustoconical surfaces of the wedging rings which can bear directly against the shaft or against an inwardly deformable hub portion which, in turn, bears against the shaft. Alternatively, the support disk or ring need not be provided with the frustoconical surfaces directly, these being provided on the shaft or a compression ring interposed between the wedging ring and the shaft or between the wedging ring and the support ring or the wheel itself when the latter forms the support ring.
Devices of the aforedescribed type have been described in a wide variety of embodiments. In German Pat. No. 874,226, for example, the stack of wedges applies radial force directly to the hub on the one hand and to the shaft on the other. The arrangement described in German Pat. No. 1,294,751 and U.S. Pat. No. 3,782,841, provides a wedge upon the sleeve and a pair of rings, forming the support rings, with complementary wedging surfaces which are drawn together by the angularly equispaced bolts. Similar arrangement is disclosed in German patent document (open application) No. 28 52 494 wherein, however, a wedge is interposed between the sleeve and the support ring. Here the wedge ring is axially displaced by the bolts relative to another wedge ring or to a wedging formation directly upon the sleeve.
In the arrangement of German Pat. No. 874,226, therefore, the torque transfer is effected directly through the wedge arrangement and possibly the support disk whereas in the other systems the wedge arrangement and support disk may lie outside the torque flow path because of the direct frictional contact of the wheel or hub and the shaft.
In these latter cases, the sleeve or hub is forced to friction-tight engagement with the shaft with the compression force being a function of the tension developed by the screws or bolts.
In practice, this tension or axial stress may vary widely and, even when the bolts are tightened with a torque wrench to a predetermined degree, the conversion of this tractive force to the radial force is found to vary widely depending upon materials and other characteristics of the wedging assembly.
As a result, the friction characteristics vary and it is difficult with existing devices to determine with any degree of precision whatsoever, the friction interaction generated by the tightening of the bolts.
As far as I am aware that has been no realistic device heretofore proposed which forms part of the clamping assembly and is capable of indicating the clamping forces developed.
Of course, as has been discussed in Maschinenmarkt, 1980 pp. 1382-1383, it is possible to control the clamping force by the torque applied to the bolts in the manner described. However, the bolts vary sufficiently with respect to the frictional characteristics of their threads, play and dimensional tolerances so that there are practically unavoidable discrepancies between the force which is developed by any clamping device of the type described and the torque applied to the bolts. In fact this discrepancy has been found to be as much as 25%.
It is possible to eliminate some of the problems by providing the screws with detectors responsive to the actual axial forces developed but these systems have not proved to be practical in applications to friction clamping arrangements of the type described above.